A flooded-type lead-acid battery includes a positive electrode plate, a negative electrode plate, a separator separating the electrode plates, and an electrolyte solution. Patent Document 1 (JP-B-3054255) discloses that: regarding a separator, polyethylene, inorganic powder made of silica or the like, and mineral oil (oil such as lubricant oil) are mixed; the mixture is molded by extrusion; and the mineral oil is then extracted. Patent Document 1 further discloses that the mineral oil is required for the acid resistance or the like of the separator, and is diffused into the electrolyte solution from the separator, which limits the content of the oil.
Patent Document 2 discloses that a negative active material of a flooded-type lead-acid battery contains carbon black, a bisphenol condensate, and a polyacrylic acid. Patent Document 2 discloses that 1.5 mass % of the carbon black, the bisphenol condensate, and the polyacrylic acid are combined to improve regenerative charge accepting performance and low-temperature high rate discharge performance and to allow the turbidity of an electrolyte solution (the concentration of the carbon black in the electrolyte solution) to be reduced.